Golf balls having two core layers formed from HNP compositions

ABSTRACT

The present invention is directed to golf balls consisting essentially of a dual-layer core and a cover. The core includes a center having a center hardness of 50 Shore C or greater and formed from a first HNP composition, and an outer core layer having a surface hardness of 75 Shore C or greater and formed from a second HNP composition. The first HNP composition has a material hardness of 55 Shore D or less and comprises a highly neutralized ethylene/(meth)acrylic acid/alkyl (meth)acrylate copolymer. The second HNP composition has a material hardness of 45 Shore D or greater and comprises a highly neutralized ethylene/(meth)acrylic acid copolymer. The material hardness of the first HNP composition is less than the material hardness of the second HNP composition. The cover includes an inner cover layer and an outer cover layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/795,086, filed Jun. 7, 2010 now U.S. Pat. No. 8,002,646, which is acontinuation of U.S. patent application Ser. No. 12/125,284, filed May22, 2008, now U.S. Pat. No. 7,731,606, which is a continuation-in-partof the following: U.S. patent application Ser. No. 11/738,740, filedApr. 23, 2007, now U.S. Pat. No. 7,468,006; U.S. patent application Ser.No. 12/048,003, filed Mar. 13, 2008; and U.S. patent application Ser.No. 12/048,021, filed Mar. 13, 2008. The entire disclosure of each ofthese related applications is hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention is directed to golf balls comprising a core and acover, wherein the core consists of a layer formed from a relativelysoft HNP composition and a layer formed from a relatively hard HNPcomposition. The present invention is not limited by which core layer isformed from the soft HNP composition and which core layer is formed fromthe hard HNP composition, so long as both layers are present in the coreof the golf ball.

BACKGROUND OF THE INVENTION

Conventional golf balls can be divided into two general classes: solidand wound. Solid golf balls include one-piece, two-piece (i.e., singlelayer core and single layer cover), and multi-layer (i.e., solid core ofone or more layers and/or a cover of one or more layers) golf balls.Wound golf balls typically include a solid, hollow, or fluid-filledcenter, surrounded by a tensioned elastomeric material, and a cover.

Golf ball core and cover layers are typically constructed with polymercompositions including, for example, polybutadiene rubber,polyurethanes, polyamides, ionomers, and blends thereof. Ionomers,particularly ethylene-based ionomers, are a preferred group of polymersfor golf ball layers because of their toughness, durability, and widerange of hardness values.

Golf ball compositions comprising highly neutralized acid polymers areknown. For example, U.S. Patent Application Publication No.2003/0130434, the entire disclosure of which is hereby incorporatedherein by reference, discloses melt-processable, highly-neutralizedethylene acid copolymers and process for making them by incorporating analiphatic, mono-functional organic acid in the acid copolymer and thenneutralizing greater than 90% of all the acid groups present. The use ofsuch compositions in various golf ball layers is disclosed. Also, U.S.Patent Application Publication No. 2005/0148725, the entire disclosureof which is hereby incorporated herein by reference, discloses ahighly-resilient thermoplastic composition comprising (a) an acidcopolymer, (b) a salt of a high molecular weight, monomeric organicacid; (c) a thermoplastic resin; (d) a cation source; and (e)optionally, a filler. The reference also discloses one-piece, two-piece,three-piece, and multi-layered golf balls comprising thehighly-resilient thermoplastic composition.

While various uses for highly neutralized acid polymers in golf ballshave been discovered, there is a need in the industry to broaden theapplicability of highly neutralized acid polymers to particular golfball constructions having desirable spin, feel, and COR properties. Thepresent invention provides such golf ball constructions through the useof a layer formed from a relatively soft HNP composition and a layerformed from a relatively hard HNP composition.

SUMMARY OF THE INVENTION

In one embodiment, the present invention is directed to a golf ballconsisting essentially of a center, an outer core layer, an inner coverlayer, and an outer cover layer. The center has a diameter of from 1.20inches to 1.30 inches, a center hardness of 50 Shore C or greater, andis formed from a first HNP composition. The first HNP composition has amaterial hardness of 55 Shore D or less and comprises a highlyneutralized ethylene/(meth)acrylic acid/alkyl (meth)acrylate copolymer.The outer core layer has a surface hardness of 75 Shore C or greater andis formed from a second HNP composition. The second HNP composition hasa material hardness of 45 Shore D or greater and comprises a highlyneutralized ethylene/(meth)acrylic acid copolymer. The Shore D hardnessof the first HNP composition is less than the Shore D hardness of thesecond HNP composition. The inner cover layer is formed from athermoplastic composition and has a material hardness less than thesurface hardness of the outer core layer. The outer cover layer isformed from a polyurethane or polyurea composition.

In one embodiment, the present invention is directed to a golf ballconsisting essentially of a center, an outer core layer, an inner coverlayer, and an outer cover layer. The center has a diameter of from 0.75inches to 1.19 inches, a center hardness of 50 Shore C or greater, andis formed from a first HNP composition. The first HNP composition has amaterial hardness of 55 Shore D or less and comprises a highlyneutralized ethylene/(meth)acrylic acid/alkyl (meth)acrylate copolymer.The outer core layer has a surface hardness of 75 Shore C or greater andis formed from a second HNP composition. The second HNP composition hasa material hardness of 45 Shore D or greater and comprises a highlyneutralized ethylene/(meth)acrylic acid copolymer. The Shore D hardnessof the first HNP composition is less than the Shore D hardness of thesecond HNP composition. The inner cover layer is formed from athermoplastic composition and has a material hardness less than thesurface hardness of the outer core layer. The outer cover layer isformed from a polyurethane or polyurea composition.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a golf ball according to oneembodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a golf ball 30 according to one embodiment of the presentinvention, including a center 32, an outer core layer 34, an inner coverlayer 36, and an outer cover layer 38. While shown in FIG. 1 as adual-layer cover, the cover may be a single-, dual-, or multi-layercover.

Golf balls of the present invention have at least two layers formed fromhighly neutralized acid polymer (“HNP”) compositions. More particularly,golf balls of the present invention have at least one layer formed froma relatively soft HNP composition, and at least one layer formed from arelatively hard HNP composition.

As used herein, “highly neutralized acid polymer” refers to an acidpolymer after at least 80%, preferably at least 90%, more preferably atleast 95%, and even more preferably 100%, of the acid groups of the acidpolymer are neutralized.

As used herein, “modulus” refers to flexural modulus as measured using astandard flex bar according to ASTM D790-B.

For purposes of the present disclosure, material hardness is measuredaccording to ASTM D2240 and generally involves measuring the hardness ofa flat “slab” or “button” formed of the material. It should beunderstood that there is a fundamental difference between “materialhardness” and “hardness as measured directly on a golf ball.” Hardnessas measured directly on a golf ball (or other spherical surface)typically results in a different hardness value than material hardness.This difference in hardness values is due to several factors including,but not limited to, ball construction (i.e., core type, number of coreand/or cover layers, etc.), ball (or sphere) diameter, and the materialcomposition of adjacent layers. It should also be understood that thetwo measurement techniques are not linearly related and, therefore, onehardness value cannot easily be correlated to the other. Unless statedotherwise, the hardness values given herein for cover materials arematerial hardness values measured according to ASTM D2240, with allvalues reported following 10 days of aging at 50% relative humidity and23° C.

The surface hardness of a golf ball layer is obtained from the averageof a number of measurements taken from opposing hemispheres of a core,taking care to avoid making measurements on the parting line of the coreor on surface defects, such as holes or protrusions. Hardnessmeasurements are made pursuant to ASTM D-2240 “Indentation Hardness ofRubber and Plastic by Means of a Durometer.” Because of the curvedsurface of a core, care must be taken to insure that the golf ball orgolf ball subassembly is centered under the durometer indentor before asurface hardness reading is obtained. A calibrated, digital durometer,capable of reading to 0.1 hardness units is used for all hardnessmeasurements and is set to take hardness readings at 1 second after themaximum reading is obtained. The digital durometer must be attached to,and its foot made parallel to, the base of an automatic stand, such thatthe weight on the durometer and attack rate conform to ASTM D-2240.

The center hardness of a core is obtained according to the followingprocedure. The core is gently pressed into a hemispherical holder havingan internal diameter approximately slightly smaller than the diameter ofthe core, such that the core is held in place in the hemisphericalportion of the holder while concurrently leaving the geometric centralplane of the core exposed. The core is secured in the holder byfriction, such that it will not move during the cutting and grindingsteps, but the friction is not so excessive that distortion of thenatural shape of the core would result. The core is secured such thatthe parting line of the core is roughly parallel to the top of theholder. The diameter of the core is measured 90 degrees to thisorientation prior to securing. A measurement is also made from thebottom of the holder to the top of the core to provide a reference pointfor future calculations. A rough cut, made slightly above the exposedgeometric center of the core using a band saw or other appropriatecutting tool, making sure that the core does not move in the holderduring this step. The remainder of the core, still in the holder, issecured to the base plate of a surface grinding machine. The exposed‘rough’ surface is ground to a smooth, flat surface, revealing thegeometric center of the core, which can be verified by measuring theheight of the bottom of the holder to the exposed surface of the core,making sure that exactly half of the original height of the core, asmeasured above, has been removed to within ±0.004 inches. Leaving thecore in the holder, the center of the core is found with a center squareand carefully marked and the hardness is measured at the center mark.

Golf ball cores of the present invention may have a zero or negative orpositive hardness gradient. A hardness gradient is defined by hardnessmeasurements made at the surface of the layer (e.g., center, outer corelayer, etc.) and radially inward towards the center of the ball,typically at 2 mm increments. For purposes of the present invention,“negative” and “positive” refer to the result of subtracting thehardness value at the innermost portion of the golf ball component fromthe hardness value at the outer surface of the component. For example,if the outer surface of a solid core has a lower hardness value than thecenter (i.e., the surface is softer than the center), the hardnessgradient will be deemed a “negative” gradient. In measuring the hardnessgradient of a core, the center hardness is first determined according tothe procedure above for obtaining the center hardness of a core. Oncethe center of the core is marked and the hardness thereof is determined,hardness measurements at any distance from the center of the core may bemeasured by drawing a line radially outward from the center mark, andmeasuring and marking the distance from the center, typically in 2 mmincrements. All hardness measurements performed on a plane passingthrough the geometric center are performed while the core is still inthe holder and without having disturbed its orientation, such that thetest surface is constantly parallel to the bottom of the holder. Thehardness difference from any predetermined location on the core iscalculated as the average surface hardness minus the hardness at theappropriate reference point, e.g., at the center of the core for asingle, solid core, such that a core surface softer than its center willhave a negative hardness gradient. Hardness gradients are disclosed morefully, for example, in U.S. patent application Ser. Nos. 11/832,163,filed on Aug. 1, 2007; 11/939,632, filed on Nov. 14, 2007; 11/939,634,filed on Nov. 14, 2007; 11/939,635, filed on Nov. 14, 2007; and11/939,637, filed on Nov. 14, 2007; the entire disclosure of each ofthese references is hereby incorporated herein by reference.

Relatively Soft HNP Composition

Relatively soft HNP compositions of the present invention have amaterial hardness of 80 Shore D or less, and preferably have a Shore Dhardness of 55 or less or a Shore D hardness within the range having alower limit of 10 or 20 or 30 or 37 or 39 or 40 or 45 and an upper limitof 48 or 50 or 52 or 55 or 60 or 80.

Relatively soft HNP compositions of the present invention comprise atleast one highly neutralized acid polymer. In a preferred embodiment,the highly neutralized acid polymer of the relatively soft HNPcomposition is a low modulus HNP having a modulus within a range havinga lower limit of 1,000 or 5,000 or 10,000 psi and an upper limit of17,000 or 25,000 or 28,000 or 30,000 or 35,000 or 45,000 or 50,000 or55,000 psi. In a particular aspect of this embodiment, the modulus ofthe low modulus HNP is at least 10% less, or at least 20% less, or atleast 25% less, or at least 30% less, or at least 35% less, than that ofthe high modulus HNP discussed below.

HNPs of the relatively soft HNP compositions of the present inventionare salts of acid copolymers. It is understood that the HNP may be ablend of two or more HNPs. The acid copolymer of the HNP is anO/X/Y-type copolymer, wherein O is an α-olefin, X is a C₃-C₈α,β-ethylenically unsaturated carboxylic acid, and Y is a softeningmonomer. O is preferably ethylene. X is preferably selected from (meth)acrylic acid, ethacrylic acid, maleic acid, crotonic acid, fumaric acid,and itaconic acid. (Meth) acrylic acid is particularly preferred. Asused herein, “(meth) acrylic acid” means methacrylic acid and/or acrylicacid. Likewise, “(meth) acrylate” means methacrylate and/or acrylate. Yis preferably an alkyl (meth) acrylate, wherein the alkyl groups havefrom 1 to 8 carbon atoms. Preferred O/X/Y-type copolymers are thosewherein O is ethylene, X is (meth) acrylic acid, and Y is selected from(meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate,methyl (meth) acrylate, and ethyl (meth) acrylate. Particularlypreferred O/X/Y-type copolymers are ethylene/(meth) acrylic acid/n-butylacrylate, ethylene/(meth) acrylic acid/methyl acrylate, andethylene/(meth) acrylic acid/ethyl acrylate.

The acid copolymer of the HNP typically includes the α-olefin in anamount of at least 15 wt %, or at least 25 wt %, or at least 40 wt %, orat least 60 wt %, based on the total weight of the acid copolymer. Theamount of C₃-C₈ α,β-ethylenically unsaturated carboxylic acid in theacid copolymer is typically within a range having a lower limit of 1 or4 or 6 or 8 or 10 or 15 wt % and an upper limit of 20 or 35 or 40 wt %,based on the total weight of the acid copolymer. The amount of softeningmonomer in the acid copolymer is typically within a range having a lowerlimit of 1 or 3 or 5 or 11 or 15 or 20 wt % and an upper limit of 23 or25 or 30 or 35 or 50 wt %, based on the total weight of the acidcopolymer.

Particularly suitable acid copolymers of the HNP of the relatively softHNP composition include very low modulus ionomer-(“VLMI-”) typeethylene-acid polymers, such as Surlyn® 6320, Surlyn® 8120, Surlyn®8320, and Surlyn® 9320. Surlyn® ionomers are commercially available fromE. I. du Pont de Nemours and Company. Also suitable are DuPont® HPF 1000and DuPont® HPF 2000, ionomeric materials commercially available from E.I. du Pont de Nemours and Company.

Additional suitable acid copolymers are disclosed, for example, in U.S.patent application Publication Nos. 2005/0148725, 2005/0020741,2004/0220343, and 2003/0130434, and U.S. Pat. Nos. 5,691,418, 6,562,906,6,653,382, 6,777,472, 6,762,246, and 6,815,480, the entire disclosuresof which are hereby incorporated herein by reference.

In a preferred embodiment, the HNP of the relatively soft HNPcomposition is formed by reacting an acid copolymer, which is optionallypartially neutralized, with a sufficient amount of cation source, in thepresence of a high molecular weight organic acid or salt thereof, suchthat at least 80%, preferably at least 90%, more preferably at least95%, and even more preferably 100%, of all acid groups present areneutralized. The acid copolymer can be reacted with the high molecularweight organic acid or salt thereof and the cation sourcesimultaneously, or the acid copolymer can be reacted with the highmolecular weight organic acid prior to the addition of the cationsource.

Suitable high molecular weight organic acids are aliphatic organicacids, aromatic organic acids, saturated monofunctional organic acids,unsaturated monofunctional organic acids, multi-unsaturatedmonofunctional organic acids, and dimerized derivatives thereof.Particular examples of suitable organic acids include, but are notlimited to, caproic acid, caprylic acid, capric acid, lauric acid,stearic acid, behenic acid, erucic acid, oleic acid, linoleic acid,myristic acid, benzoic acid, palmitic acid, phenylacetic acid,naphthalenic acid, dimerized derivatives thereof, and combinationsthereof. Salts of high molecular weight organic acids comprise thesalts, particularly the barium, lithium, sodium, zinc, bismuth,chromium, cobalt, copper, potassium, strontium, titanium, tungsten,magnesium, and calcium salts, of aliphatic organic acids, aromaticorganic acids, saturated monofunctional organic acids, unsaturatedmonofunctional organic acids, multi-unsaturated monofunctional organicacids, dimerized derivatives thereof, and combinations thereof. Suitableorganic acids and salts thereof are more fully described, for example,in U.S. Pat. No. 6,756,436, the entire disclosure of which is herebyincorporated herein by reference.

Suitable cation sources include metal ions and compounds of alkalimetals, alkaline earth metals, and transition metals; metal ions andcompounds of rare earth elements; silicone, silane, and silicatederivatives and complex ligands; and combinations thereof. Preferredcation sources are metal ions and compounds of magnesium, sodium,potassium, cesium, calcium, barium, manganese, copper, zinc, tin,lithium, and rare earth metals. The acid copolymer may be at leastpartially neutralized prior to contacting the acid copolymer with thecation source to form the HNP. Methods of preparing ionomers are wellknown, and are disclosed, for example, in U.S. Pat. No. 3,264,272, theentire disclosure of which is hereby incorporated herein by reference.The acid copolymer can be a direct copolymer wherein the polymer ispolymerized by adding all monomers simultaneously, as disclosed, forexample, in U.S. Pat. No. 4,351,931, the entire disclosure of which ishereby incorporated herein by reference. Alternatively, the acidcopolymer can be a graft copolymer wherein a monomer is grafted onto anexisting polymer, as disclosed, for example, in U.S. Patent ApplicationPublication No. 2002/0013413, the entire disclosure of which is herebyincorporated herein by reference.

Relatively soft HNP compositions of the present invention optionallycontain one or more melt flow modifiers. The amount of melt flowmodifier in the composition is readily determined such that the meltflow index of the composition is at least 0.1 g/10 min, preferably from0.5 g/10 min to 10.0 g/10 min, and more preferably from 1.0 g/10 min to6.0 g/10 min, as measured using ASTM D-1238, condition E, at 190° C.,using a 2160 gram weight.

Suitable melt flow modifiers include, but are not limited to, highmolecular weight organic acids and salts thereof, polyamides,polyesters, polyacrylates, polyurethanes, polyethers, polyureas,polyhydric alcohols, and combinations thereof. Suitable organic acidsare aliphatic organic acids, aromatic organic acids, saturatedmono-functional organic acids, unsaturated monofunctional organic acids,multi-unsaturated mono-functional organic acids, and dimerizedderivatives thereof. Particular examples of suitable organic acidsinclude, but are not limited to, caproic acid, caprylic acid, capricacid, lauric acid, stearic acid, behenic acid, erucic acid, oleic acid,linoleic acid, myristic acid, benzoic acid, palmitic acid, phenylaceticacid, naphthalenoic acid, dimerized derivatives thereof. Suitableorganic acids are more fully described, for example, in U.S. Pat. No.6,756,436, the entire disclosure of which is hereby incorporated hereinby reference.

Additional melt flow modifiers suitable for use in compositions of thepresent invention, include the non-fatty acid melt flow modifiersdescribed in copending U.S. patent application Ser. Nos. 11/216,725 and11/216,726, the entire disclosures of which are hereby incorporatedherein by reference.

Relatively soft HNP compositions of the present invention optionallyinclude additive(s) and/or filler(s) in an amount of 50 wt % or less, or30 wt % or less, or 15 wt % or less, based on the total weight of therelatively soft HNP composition. Suitable additives and fillers include,but are not limited to, chemical blowing and foaming agents, opticalbrighteners, coloring agents, fluorescent agents, whitening agents, UVabsorbers, light stabilizers, defoaming agents, processing aids, mica,talc, nano-fillers, antioxidants, stabilizers, softening agents,fragrance components, plasticizers, impact modifiers, TiO₂, acidcopolymer wax, surfactants, and fillers, such as zinc oxide, tin oxide,barium sulfate, zinc sulfate, calcium oxide, calcium carbonate, zinccarbonate, barium carbonate, clay, tungsten, tungsten carbide, silica,lead silicate, regrind (recycled material), and mixtures thereof.Suitable additives are more fully described in, for example, U.S. PatentApplication Publication No. 2003/0225197, the entire disclosure of whichis hereby incorporated herein by reference.

Relatively soft HNP compositions of the present invention optionallycontain a high modulus HNP.

In a particular embodiment, the relatively soft HNP composition has amoisture vapor transmission rate of 8 g-mil/100 in²/day or less (i.e.,3.2 g-mm/m²·day or less), or 5 g-mil/100 in²/day or less (i.e., 2.0g-mm/m²·day or less), or 3 g-mil/100 in²/day or less (i.e., 1.2g-mm/m²·day or less), or 2 g-mil/100 in²/day or less (i.e., 0.8g-mm/m²·day or less), or 1 g-mil/100 in²/day or less (i.e., 0.4g-mm/m²·day or less), or less than 1 g-mil/100 in²/day (i.e., less than0.4 g-mm/m²·day). As used herein, moisture vapor transmission rate(“MVTR”) is given in g-mil/100 in²/day, and is measured at 20° C. andaccording to ASTM F1249-99. In a preferred aspect of this embodiment,the relatively soft HNP composition comprises a low modulus HNP preparedusing a cation source which is less hydrophilic than conventionalmagnesium-based cation sources. Suitable moisture resistant HNPcompositions are disclosed, for example, in U.S. Patent ApplicationPublication Nos. 2005/0267240, 2006/0106175 and 2006/0293464, the entiredisclosures of which are hereby incorporated herein by reference.

In another particular embodiment, a sphere formed from the relativelysoft HNP composition has a compression of 80 or less, or 70 or less, or65 or less, or 60 or less, or 50 or less, or 40 or less, or 30 or less,or 20 or less.

Relatively soft HNP compositions of the present invention are notlimited by any particular method or any particular equipment for makingthe compositions. In a preferred embodiment, the composition is preparedby the following process. The acid polymer(s), preferably a VLMI-typeethylene-acid terpolymer, high molecular weight organic acid(s) orsalt(s) thereof, and optionally additive(s)/filler(s) are simultaneouslyor individually fed into a melt extruder, such as a single or twin screwextruder. A suitable amount of cation source is simultaneously orsubsequently added such that at least 80%, preferably at least 90%, morepreferably at least 95%, and even more preferably 100%, of all acidgroups present are neutralized. The acid polymer may be at leastpartially neutralized prior to the above process. The components areintensively mixed prior to being extruded as a strand from the die-head.

Relatively soft HNP compositions of the present invention may be blendedwith one or more additional polymers, such as thermoplastic polymers andelastomers. Examples of thermoplastic polymers suitable for blendinginclude, but are not limited to, bimodal ionomers (e.g., as disclosed inU.S. Patent Application Publication No. 2004/0220343 and U.S. Pat. Nos.6,562,906, 6,762,246 and 7,273,903, the entire disclosures of which arehereby incorporated herein by reference), ionomers modified with rosins(e.g., as disclosed in U.S. Patent Application Publication No.2005/0020741, the entire disclosure of which is hereby incorporated byreference), soft and resilient ethylene copolymers (e.g., as disclosedU.S. Patent Application Publication No. 2003/0114565, the entiredisclosure of which is hereby incorporated herein by reference)polyolefins, polyamides, polyesters, polyethers, polycarbonates,polysulfones, polyacetals, polylactones, acrylonitrile-butadiene-styreneresins, polyphenylene oxide, polyphenylene sulfide,styrene-acrylonitrile resins, styrene maleic anhydride, polyimides,aromatic polyketones, ionomers and ionomeric precursors, acidcopolymers, conventional HNPs, polyurethanes, grafted and non-graftedmetallocene-catalyzed polymers, single-site catalyst polymerizedpolymers, high crystalline acid polymers, cationic ionomers, andcombinations thereof. Particular polyolefins suitable for blendinginclude one or more, linear, branched, or cyclic, C₂-C₄₀ olefins,particularly polymers comprising ethylene or propylene copolymerizedwith one or more C₂-C₄₀ olefins, C₃-C₂₀ α-olefins, or C₃-C₁₀ α-olefins.Particular conventional HNPs suitable for blending include, but are notlimited to, one or more of the HNPs disclosed in U.S. Pat. Nos.6,756,436, 6,894,098, and 6,953,820, the entire disclosures of which arehereby incorporated herein by reference. Examples of elastomers suitablefor blending with the invention polymers include natural and syntheticrubbers, including, but not limited to, ethylene propylene rubber(“EPR”), ethylene propylene diene rubber (“EPDM”), styrenic blockcopolymer rubbers (such as SI, SIS, SB, SBS, SIBS, and the like, where“S” is styrene, “I” is isobutylene, and “B” is butadiene), butyl rubber,halobutyl rubber, copolymers of isobutylene and para-alkylstyrene,halogenated copolymers of isobutylene and para-alkylstyrene, naturalrubber, polyisoprene, copolymers of butadiene with acrylonitrile,polychloroprene, alkyl acrylate rubber, chlorinated isoprene rubber,acrylonitrile chlorinated isoprene rubber, and polybutadiene rubber (cisand trans). Additional suitable blend polymers include those describedin U.S. Pat. No. 5,981,658, for example at column 14, lines 30 to 56,the entire disclosure of which is hereby incorporated herein byreference. The blends described herein may be produced by post-reactorblending, by connecting reactors in series to make reactor blends, or byusing more than one catalyst in the same reactor to produce multiplespecies of polymer. The polymers may be mixed prior to being put into anextruder, or they may be mixed in an extruder.

Particularly suitable relatively soft HNP compositions include, but arenot limited to, the highly-resilient thermoplastic compositionsdisclosed in U.S. Patent Application Publication No. 2005/0148725; thehighly-neutralized ethylene copolymers disclosed in U.S. Pat. Nos.6,653,382 and 6,777,472, and U.S. Patent Application Publication No.2003/0130434; and the highly-resilient thermoplastic elastomercompositions disclosed in U.S. Pat. No. 6,815,480; the entiredisclosures of which are hereby incorporated herein by reference.

Relatively Hard HNP Composition

Relatively hard HNP compositions of the present invention have a Shore Dhardness of 35 or greater, and preferably have a Shore D hardness of 45or greater or a Shore D hardness with the range having a lower limit of45 or 50 or 55 or 57 or 58 or 60 or 65 or 70 or 75 and an upper limit of80 or 85 or 90 or 95.

Relatively hard HNP compositions of the present invention comprise atleast one highly neutralized acid polymer. In a preferred embodiment,the highly neutralized acid polymer of the relatively hard HNPcomposition is a high modulus HNP having a modulus within a range havinga lower limit of 25,000 or 27,000 or 30,000 or 40,000 or 45,000 or50,000 or 55,000 or 60,000 psi and an upper limit of 72,000 or 75,000 or100,000 or 150,000 psi.

HNPs of the relatively hard HNP compositions of the present inventionare salts of acid copolymers. It is understood that the HNP may be ablend of two or more HNPs. Preferred acid copolymers are copolymers ofan α-olefin and a C₃-C₈ α,β-ethylenically unsaturated carboxylic acid.The acid is typically present in the acid copolymer in an amount withina range having a lower limit of 1 or 10 or 12 or 15 or 20 wt % and anupper limit of 25 or 30 or 35 or 40 wt %, based on the total weight ofthe acid copolymer. The α-olefin is preferably selected from ethyleneand propylene. The acid is preferably selected from (meth) acrylic acid,ethacrylic acid, maleic acid, crotonic acid, fumaric acid, and itaconicacid. (Meth) acrylic acid is particularly preferred. In a preferredembodiment, the HNP of the relatively hard HNP composition has a higherlevel of acid than the HNP of the relatively soft HNP composition.

Suitable acid copolymers include partially neutralized acid polymers.Examples of suitable partially neutralized acid polymers include, butare not limited to, Surlyn® ionomers, commercially available from E. I.du Pont de Nemours and Company; AClyn® ionomers, commercially availablefrom Honeywell International Inc.; and Iotek® ionomers, commerciallyavailable from ExxonMobil Chemical Company. Also suitable are DuPont®HPF 1000 and DuPont® HPF 2000, ionomeric materials commerciallyavailable from E. I. du Pont de Nemours and Company. Additional suitableacid polymers are more fully described, for example, in U.S. Pat. Nos.6,562,906, 6,762,246, and 6,953,820 and U.S. Patent ApplicationPublication Nos. 2005/0049367, 2005/0020741, and 2004/0220343, theentire disclosures of which are hereby incorporated herein by reference.

In a preferred embodiment, the HNP of the relatively soft HNPcomposition is formed by reacting an acid copolymer with a sufficientamount of cation source such that at least 80%, preferably at least 90%,more preferably at least 95%, and even more preferably 100%, of all acidgroups present are neutralized. Suitable cation sources include metalions and compounds of alkali metals, alkaline earth metals, andtransition metals; metal ions and compounds of rare earth elements;silicone, silane, and silicate derivatives and complex ligands; andcombinations thereof. Preferred cation sources are metal ions andcompounds of magnesium, sodium, potassium, cesium, calcium, barium,manganese, copper, zinc, tin, lithium, and rare earth metals. Metal ionsand compounds of calcium and magnesium are particularly preferred. Theacid copolymer may be at least partially neutralized prior to contactingthe acid copolymer with the cation source to form the HNP. As previouslystated, methods of preparing ionomers, and the acid copolymers on whichionomers are based, are disclosed, for example, in U.S. Pat. Nos.3,264,272, and 4,351,931, and U.S. Patent Application Publication No.2002/0013413.

Relatively hard HNP compositions of the present invention optionallycontain one or more melt flow modifiers. The amount of melt flowmodifier in the composition is readily determined such that the meltflow index of the composition is at least 0.1 g/10 min, preferably from0.5 g/10 min to 10.0 g/10 min, and more preferably from 1.0 g/10 min to6.0 g/10 min, as measured using ASTM D-1238, condition E, at 190° C.,using a 2160 gram weight.

Suitable melt flow modifiers include, but are not limited to, highmolecular weight organic acids and salts thereof, polyamides,polyesters, polyacrylates, polyurethanes, polyethers, polyureas,polyhydric alcohols, and combinations thereof. Suitable organic acidsare aliphatic organic acids, aromatic organic acids, saturatedmono-functional organic acids, unsaturated monofunctional organic acids,multi-unsaturated mono-functional organic acids, and dimerizedderivatives thereof. Particular examples of suitable organic acidsinclude, but are not limited to, caproic acid, caprylic acid, capricacid, lauric acid, stearic acid, behenic acid, erucic acid, oleic acid,linoleic acid, myristic acid, benzoic acid, palmitic acid, phenylaceticacid, naphthalenoic acid, dimerized derivatives thereof. Suitableorganic acids are more fully described, for example, in U.S. Pat. No.6,756,436, the entire disclosure of which is hereby incorporated hereinby reference.

Additional melt flow modifiers suitable for use in compositions of thepresent invention, include the non-fatty acid melt flow modifiersdescribed in copending U.S. patent application Ser. Nos. 11/216,725 and11/216,726, the entire disclosures of which are hereby incorporatedherein by reference.

Relatively hard HNP compositions of the present invention optionallyinclude additive(s) and/or filler(s) in an amount within a range havinga lower limit of 0 or 5 or 10 wt %, and an upper limit of 25 or 30 or 50wt %, based on the total weight of the relatively hard HNP composition.Suitable additives and fillers include those previously described assuitable for the relatively soft HNP compositions of the presentinvention.

Relatively hard HNP compositions of the present invention optionallycontain a low modulus HNP.

In a particular embodiment, the relatively hard HNP composition has anMVTR of 8 g-mil/100 in²/day or less (i.e., 3.2 g-mm/m²·day or less), or5 g-mil/100 in²/day or less (i.e., 2.0 g-mm/m²·day or less), or 3g-mil/100 in²/day or less (i.e., 1.2 g-mm/m²·day or less), or 2g-mil/100 in²/day or less (i.e., 0.8 g-mm/m²·day or less), or 1g-mil/100 in²/day or less (i.e., 0.4 g-mm/m²·day or less), or less than1 g-mil/100 in²/day (i.e., less than 0.4 g-mm/m² day). In a preferredaspect of this embodiment, the relatively hard HNP composition comprisesa high modulus HNP prepared using a cation source which is lesshydrophilic than conventional magnesium-based cation sources. Suitablemoisture resistant HNP compositions are disclosed, for example, incopending U.S. patent application Ser. No. 11/270,066 and U.S. PatentApplication Publication No. 2005/0267240, the entire disclosures ofwhich are hereby incorporated herein by reference.

In another particular embodiment, a sphere formed from the relativelyhard HNP composition has a compression of 70 or greater, or 80 orgreater, or a compression within a range having a lower limit of 70 or80 or 90 or 100 and an upper limit of 110 or 130 or 140.

Relatively hard HNP compositions of the present invention are notlimited by any particular method or any particular equipment for makingthe compositions. In a preferred embodiment, the composition is preparedby the following process. The acid polymer(s), preferably anethylene/(meth) acrylic acid copolymer, optional melt flow modifier(s),and optional additive(s)/filler(s) are simultaneously or individuallyfed into a melt extruder, such as a single or twin screw extruder. Asuitable amount of cation source is then added such that at least 80%,preferably at least 90%, more preferably at least 95%, and even morepreferably 100%, of all acid groups present are neutralized. The acidpolymer may be at least partially neutralized prior to the aboveprocess. The components are intensively mixed prior to being extruded asa strand from the die-head.

In another preferred embodiment, the relatively hard HNP composition isformed by combining a low modulus HNP with a sufficient amount of one ormore additional material(s), including, but not limited to, additives,fillers, and polymeric materials, to increase the modulus such that theresulting composition has a modulus as described above for the highmodulus HNP.

Relatively hard HNP compositions of the present invention may be blendedwith one or more additional polymers, such as thermoplastic polymers andelastomers. Examples of thermoplastic polymers and elastomers suitablefor blending include those previously described as suitable for blendingwith the relatively soft HNP compositions of the present invention.

HNP compositions of the present invention, in the neat (i.e., unfilled)form, preferably have a specific gravity of from 0.95 g/cc to 0.99 g/cc.Any suitable filler, flake, fiber, particle, or the like, of an organicor inorganic material may be added to the HNP composition to increase ordecrease the specific gravity, particularly to adjust the weightdistribution within the golf ball, as further disclosed in U.S. Pat.Nos. 6,494,795, 6,547,677, 6,743,123, 7,074,137, and 6,688,991, theentire disclosures of which are hereby incorporated herein by reference.

Golf Ball Applications

Golf balls of the present invention comprise at least one layer formedfrom a relatively soft HNP composition and at least one layer formedfrom a relatively hard HNP composition. In a preferred embodiment, thepresent invention provides a golf ball having a dual-layer core and adual-layer cover, wherein the dual-layer core includes a layer formedfrom a relatively soft HNP composition and a layer formed from arelatively hard HNP composition.

In the embodiments disclosed herein, the relatively soft HNP compositionand/or the relatively hard HNP composition can be either foamed orfilled with density adjusting materials to provide desirable golf ballperformance characteristics.

Golf balls having a layer formed from a relatively soft HNP compositionand a layer formed from a relatively hard HNP composition are furtherdisclosed, for example, in U.S. Patent Application Publication No.2007/0207879, the entire disclosure of which is hereby incorporatedherein by reference.

In one embodiment, the present invention provides a golf ball having adual-layer core, wherein the core includes a center and an outer corelayer. In a particular aspect of this embodiment, the center is formedfrom a relatively soft HNP composition and the outer core layer isformed from a relatively hard HNP composition. In another particularaspect of this embodiment, the center is formed from a relatively hardHNP composition and the outer core layer is formed from a relativelysoft HNP composition.

In one embodiment, the present invention is directed to a golf ballcomprising a center, an outer core layer, and one or more cover layers.In a particular aspect of this embodiment, the golf ball has one or moreof the following properties:

-   -   (a) a center having a diameter within a range having a lower        limit of 0.500 or 0.750 or 1.000 or 1.100 or 1.200 inches and an        upper limit of 1.300 or 1.350 or 1.400 or 1.550 or 1.570 or        1.580 inches;    -   (b) a center having a diameter within a range having a lower        limit of 0.750 or 0.850 or 0.875 inches and an upper limit of        1.125 or 1.150 or 1.190 inches;    -   (c) an outer core layer enclosing the center such that the        dual-layer core has an overall diameter within a range having a        lower limit of 1.400 or 1.500 or 1.510 or 1.520 or 1.525 inches        and an upper limit of 1.540 or 1.550 or 1.555 or 1.560 or 1.590        inches, or an outer core layer having a thickness within a range        having a lower limit of 0.020 or 0.025 or 0.032 inches and an        upper limit of 0.310 or 0.440 or 0.560 inches;    -   (d) a center having a center hardness of 50 Shore C or greater,        or 55 Shore C or greater, or 60 Shore C or greater, or a center        hardness within a range having a lower limit of 50 or 55 or 60        Shore C and an upper limit of 65 or 70 or 80 Shore C;    -   (e) a center having a surface hardness of 65 Shore C or greater,        or 70 Shore C or greater, or a surface hardness within a range        having a lower limit of 55 or 60 or 65 or 70 or 75 Shore C and        an upper limit of 80 or 85 Shore C;    -   (f) an outer core layer having a surface hardness of 75 Shore C        or greater, or 80 Shore C or greater, or greater than 80 Shore        C, or 85 Shore C or greater, or greater than 85 Shore C, or 87        Shore C or greater, or greater than 87 Shore C, or 89 Shore C or        greater, or greater than 89 Shore C, or 90 Shore C or greater,        or greater than 90 Shore C, or a surface hardness within a range        having a lower limit of 75 or 80 or 85 Shore C and an upper        limit of 95 Shore C;    -   (g) a center having a surface hardness greater than or equal to        the center hardness of the center;    -   (h) a center having a positive hardness gradient wherein the        surface hardness of the center is at least 10 Shore C units        greater than the center hardness of the center;    -   (i) an outer core layer having a surface hardness greater than        or equal to the surface hardness and center hardness of the        center;    -   (j) a core having a positive hardness gradient wherein the        surface hardness of the outer core layer is at least 20 Shore C        units greater, or at least 25 Shore C units greater, or at least        30 Shore C units greater, than the center hardness of the        center;    -   (k) a center having a compression of 40 or less; and    -   (l) a center having a compression of from 20 to 40.

The weight distribution of cores disclosed herein can be varied toachieve certain desired parameters, such as spin rate, compression, andinitial velocity.

Golf ball cores of the present invention typically have an overall corecompression of less than 100, or a compression of 87 or less, or anoverall core compression within a range having a lower limit of 20 or 50or 60 or 65 or 70 or 75 and an upper limit of 80 or 85 or 90 or 100 or110 or 120, or an overall core compression of about 80. Compression isan important factor in golf ball design. For example, the compression ofthe core can affect the ball's spin rate off the driver and the feel. Asdisclosed in Jeff Dalton's Compression by Any Other Name, Science andGolf IV, Proceedings of the World Scientific Congress of Golf (EricThain ed., Routledge, 2002) (“J. Dalton”), several different methods canbe used to measure compression, including Atti compression, Riehlecompression, load/deflection measurements at a variety of fixed loadsand offsets, and effective modulus. For purposes of the presentinvention, “compression” refers to Atti compression and is measuredaccording to a known procedure, using an Atti compression test device,wherein a piston is used to compress a ball against a spring. The travelof the piston is fixed and the deflection of the spring is measured. Themeasurement of the deflection of the spring does not begin with itscontact with the ball; rather, there is an offset of approximately thefirst 1.25 mm (0.05 inches) of the spring's deflection. Very lowstiffness cores will not cause the spring to deflect by more than 1.25mm and therefore have a zero compression measurement. The Atticompression tester is designed to measure objects having a diameter of42.7 mm (1.68 inches); thus, smaller objects, such as golf ball cores,must be shimmed to a total height of 42.7 mm to obtain an accuratereading. Conversion from Atti compression to Riehle (cores), Riehle(balls), 100 kg deflection, 130-10 kg deflection or effective moduluscan be carried out according to the formulas given in J. Dalton.

Golf ball cores of the present invention typically have a coefficient ofrestitution (“COR”) at 125 ft/s of at least 0.75, preferably at least0.78, and more preferably at least 0.79. COR, as used herein, isdetermined according to a known procedure wherein a golf ball or golfball subassembly (e.g., a golf ball core) is fired from an air cannon ata given velocity (125 ft/s for purposes of the present invention).Ballistic light screens are located between the air cannon and the steelplate to measure ball velocity. As the ball travels toward the steelplate, it activates each light screen, and the time at each light screenis measured. This provides an incoming transit time period proportionalto the ball's incoming velocity. The ball impacts the steel plate andrebounds though the light screens, which again measure the time periodrequired to transit between the light screens. This provides an outgoingtransit time period proportional to the ball's outgoing velocity. COR isthen calculated as the ratio of the outgoing transit time period to theincoming transit time period, COR=T_(out)/T_(in).

Cores of the present invention are enclosed with a cover, which may be asingle-, dual-, or multi-layer cover.

In a particular embodiment, the cover is a dual-layer cover comprisingan inner cover layer and an outer cover layer. In a particular aspect ofthis embodiment, the surface hardness of the outer core layer is greaterthan the material hardness of the inner cover layer. In anotherparticular aspect of this embodiment, the surface hardness of the outercore layer is greater than both the inner cover layer and the outercover layer.

The inner cover layer preferably has a material hardness of 95 Shore Cor less, or less than 95 Shore C, or 92 Shore C or less, or 90 Shore Cor less, or has a material hardness within a range having a lower limitof 70 or 75 or 80 or 84 or 85 Shore C and an upper limit of 90 or 92 or95 Shore C. The thickness of the inner cover layer is preferably withina range having a lower limit of 0.010 or 0.015 or 0.020 or 0.030 inchesand an upper limit of 0.035 or 0.045 or 0.080 or 0.120 inches.

The outer cover layer preferably has a material hardness of 85 Shore Cor less. The thickness of the outer cover layer is preferably within arange having a lower limit of 0.010 or 0.015 or 0.025 inches and anupper limit of 0.035 or 0.040 or 0.055 or 0.080 inches.

Suitable cover layer materials for the golf balls disclosed hereininclude, but are not limited to, ionomer resin and blends thereof(particularly Surlyn® ionomer resin), polyurethanes, polyureas,(meth)acrylic acid, thermoplastic rubber polymers, polyethylene, andsynthetic or natural vulcanized rubber, such as balata. Suitablecommercially available ionomeric cover materials include, but are notlimited to, Surlyn® ionomer resins and DuPont® HPF 1000 and HPF 2000,commercially available from E. I. du Pont de Nemours and Company; andIotek® ionomers, commercially available from ExxonMobil ChemicalCompany.

Particularly suitable outer cover layer materials include relativelysoft polyurethanes and polyureas. When used as cover layer materials,polyurethanes and polyureas can be thermoset or thermoplastic. Thermosetmaterials can be formed into golf ball layers by conventional casting orreaction injection molding techniques. Thermoplastic materials can beformed into golf ball layers by conventional compression or injectionmolding techniques. Light stable polyureas and polyurethanes arepreferred for the outer cover layer material. Additional suitable coverand rubber core materials are disclosed, for example, in U.S. PatentApplication Publication No. 2005/0164810, U.S. Pat. No. 5,919,100, andPCT Publications WO00/23519 and WO00/29129, the entire disclosures ofwhich are hereby incorporated herein by reference. In embodiments of thepresent invention wherein a golf ball having a single layer cover isprovided, the cover layer material is preferably selected frompolyurethane and polyurea. In embodiments of the present inventionwherein a golf ball having a dual cover is provided, the inner coverlayer is preferably a high modulus thermoplastic, and the outer coverlayer is preferably selected from polyurethane and polyurea.

Suitable cover layer materials also include blends of ionomers withthermoplastic elastomers. Suitable ionomeric cover materials are furtherdisclosed, for example, in U.S. Pat. Nos. 6,653,382, 6,756,436,6,894,098, 6,919,393, and 6,953,820, the entire disclosures of which arehereby incorporated by reference. Suitable polyurethane cover materialsare further disclosed in U.S. Pat. Nos. 5,334,673, 6,506,851, 6,756,436,and 7,105,623, the entire disclosures of which are hereby incorporatedherein by reference. Suitable polyurea cover materials are furtherdisclosed in U.S. Pat. Nos. 5,484,870 and 6,835,794, the entiredisclosures of which are hereby incorporated herein by reference.Suitable polyurethane-urea hybrids are blends or copolymers comprisingurethane or urea segments as disclosed in U.S. Patent ApplicationPublication No. 2007/0117923, the entire disclosure of which is herebyincorporated herein by reference. Additional suitable cover materialsare disclosed, for example, in U.S. Patent Application Publication No.2005/0164810, U.S. Pat. No. 5,919,100, and PCT Publications WO00/23519and WO00/29129, the entire disclosures of which are hereby incorporatedherein by reference.

In a particular embodiment, the cover is a single layer preferablyformed from an ionomeric composition. The single layer cover preferablyhas a surface hardness of 65 Shore D or less, or 60 Shore D or less, or45 Shore D or less, or 40 Shore D or less, or from 25 Shore D to 40Shore D, or from 30 Shore D to 40 Shore D and a thickness within a rangehaving a lower limit of 0.010 or 0.015 or 0.020 or 0.025 or 0.030 or0.055 or 0.060 inches and an upper limit of 0.065 or 0.080 or 0.090 or0.100 or 0.110 or 0.120 or 0.140 inches. The flexural modulus of thecover, as measured by ASTM D6272-98 Procedure B, is preferably 500 psior greater, or from 500 psi to 150,000 psi.

In another particular embodiment, the cover is a dual-layer coverconsisting of an inner cover layer and an outer cover layer. The innercover layer is preferably formed from an ionomeric composition, andpreferably has a surface hardness within a range having a lower limit of30 or 40 or 55 or 60 or 65 Shore D and an upper limit of 66 or 68 or 70or 75 Shore D, and a thickness within a range having a lower limit of0.010 or 0.015 or 0.020 or 0.030 inches and an upper limit of 0.035 or0.040 or 0.045 or 0.050 or 0.055 or 0.075 or 0.080 or 0.110 or 0.120inches. The outer cover layer is preferably formed from a castable orreaction injection moldable polyurethane, polyurea, or copolymer orhybrid of polyurethane/polyurea. Such cover material is preferablythermosetting, but may be thermoplastic, and preferably has a surfacehardness within a range having a lower limit of 30 or 40 Shore D and anupper limit of 52 or 58 or 62 or 66 or 72 or 75 Shore D. The outer coverlayer preferably has a thickness within a range having a lower limit of0.010 or 0.015 or 0.025 inches and an upper limit of 0.035 or 0.040 or0.045 or 0.050 or 0.055 or 0.075 or 0.080 or 0.115 inches. The two-layercover preferably has an overall thickness within a range having a lowerlimit of 0.010 or 0.015 or 0.020 or 0.025 or 0.030 or 0.055 or 0.060inches and an upper limit of 0.065 or 0.075 or 0.080 or 0.090 or 0.100or 0.110 or 0.120 or 0.140 inches.

The ionomeric composition of the inner cover layer is preferablyselected from:

-   -   (a) a composition comprising a “high acid ionomer” (i.e., having        an acid content of greater than 16 wt %), such as Surlyn 8150®,        a copolymer of ethylene and methacrylic acid, having an acid        content of 19 wt %, which is 45% neutralized with sodium,        commercially available from E. I. du Pont de Nemours and        Company;    -   (b) a composition comprising a high acid ionomer and a maleic        anhydride-grafted non-ionomeric polymer (e.g., Fusabond 572D®, a        maleic anhydride-grafted, metallocene-catalyzed ethylene-butene        copolymer having about 0.9 wt % maleic anhydride grafted onto        the copolymer, commercially available from E. I. du Pont de        Nemours and Company). A particularly preferred blend of high        acid ionomer and maleic anhydride-grafted polymer is a 84 wt        %/16 wt % blend of Surlyn 8150® and Fusabond 572D®. Blends of        high acid ionomers with maleic anhydride-grafted polymers are        further disclosed, for example, in U.S. Pat. Nos. 6,992,135 and        6,677,401, the entire disclosures of which are hereby        incorporated herein by reference;    -   (c) a composition comprising a 50/45/5 blend of Surlyn®        8940/Surlyn® 9650/Nucrel® 960, preferably having a material        hardness of from 80 to 85 Shore C;    -   (d) a composition comprising a 50/25/25 blend of Surlyn®        8940/Surlyn® 9650/Surlyn® 9910, preferably having a material        hardness of about 90 Shore C; and    -   (e) a composition comprising a 50/50 blend of Surlyn®        8940/Surlyn® 9650, preferably having a material hardness of        about 86 Shore C.

Surlyn® 8940 is an E/MAA copolymer in which the MAA acid groups havebeen partially neutralized with sodium ions. Surlyn® 9650 and Surlyn®9910 are two different grades of E/MAA copolymer in which the MAA acidgroups have been partially neutralized with zinc ions. Nucrel® 960 is anE/MAA copolymer resin nominally made with 15 wt % methacrylic acid.Surlyn® 8940, Surlyn® 9650, Surlyn® 9910, and Nucrel® 960 arecommercially available from E. I. du Pont de Nemours and Company.

Non-limiting examples of preferred inner cover layer materials are shownin the Examples below.

The inner cover layer material may include a flow modifier, such as, butnot limited to, Nucrel® acid copolymer resins, and particularly Nucrel®960. Nucrel® acid copolymer resins are commercially available from E. I.du Pont de Nemours and Company.

The outer cover layer is preferably formed from a composition comprisingpolyurethane, polyurea, or a copolymer or hybrid ofpolyurethane/polyurea. The outer cover layer material may bethermoplastic or thermoset.

A moisture vapor barrier layer is optionally employed between the coreand the cover. Moisture vapor barrier layers are further disclosed, forexample, in U.S. Pat. Nos. 6,632,147, 6,932,720, 7,004,854, and7,182,702, the entire disclosures of which are hereby incorporatedherein by reference.

The present invention is not limited by any particular process forforming the golf ball layer(s). It should be understood that thelayer(s) can be formed by any suitable technique, including injectionmolding, compression molding, casting, and reaction injection molding.

When injection molding is used, the composition is typically in apelletized or granulated form that can be easily fed into the throat ofan injection molding machine wherein it is melted and conveyed via ascrew in a heated barrel at temperatures of from 150° F. to 600° F.,preferably from 200° F. to 500° F. The molten composition is ultimatelyinjected into a closed mold cavity, which may be cooled, at ambient orat an elevated temperature, but typically the mold is cooled to atemperature of from 50° F. to 70° F. After residing in the closed moldfor a time of from 1 second to 300 seconds, preferably from 20 secondsto 120 seconds, the core and/or core plus one or more additional core orcover layers is removed from the mold and either allowed to cool atambient or reduced temperatures or is placed in a cooling fluid such aswater, ice water, dry ice in a solvent, or the like.

When compression molding is used to form a center, the composition isfirst formed into a preform or slug of material, typically in acylindrical or roughly spherical shape at a weight slightly greater thanthe desired weight of the molded core. Prior to this step, thecomposition may be first extruded or otherwise melted and forced througha die after which it is cut into a cylindrical preform. It is thatpreform that is then placed into a compression mold cavity andcompressed at a mold temperature of from 150° F. to 400° F., preferablyfrom 250° F. to 350° F., and more preferably from 260° F. to 295° F.When compression molding a core or cover layer of an HNP composition, ahalf-shell is first formed via injection molding and then a corecomprising one or more layers is enclosed within two half shells andthen compression molded in a similar manner to the process previouslydescribed.

Reaction injection molding processes are further disclosed, for example,in U.S. Pat. Nos. 6,083,119, 7,338,391, 7,282,169, 7,281,997 and U.S.Patent Application Publication No. 2006/0247073, the entire disclosuresof which are hereby incorporated herein by reference.

Golf balls of the present invention typically have a compression of 120or less, or a compression within a range having a lower limit of 50 or60 or 65 or 75 or 80 or 90 and an upper limit of 95 or 100 or 105 or 110or 115 or 120. Golf balls of the present invention typically have a CORat 125 ft/s of at least 0.75, preferably at least 0.78, and morepreferably at least 0.79.

Golf balls of the present invention will typically have dimple coverageof 60% or greater, preferably 65% or greater, and more preferably 75% orgreater. The United States Golf Association specifications limit theminimum size of a competition golf ball to 1.680 inches. There is nospecification as to the maximum diameter, and golf balls of any size canbe used for recreational play. Golf balls of the present invention canhave an overall diameter of any size. The preferred diameter of thepresent golf balls is from 1.680 inches to 1.800 inches. Morepreferably, the present golf balls have an overall diameter of from1.680 inches to 1.760 inches, and even more preferably from 1.680 inchesto 1.740 inches.

Golf balls of the present invention preferably have a moment of inertia(“MOT”) of 70-95 g·cm², preferably 75-93 g·cm², and more preferably76-90 g·cm². For low MOT embodiments, the golf ball preferably has anMOT of 85 g·cm² or less, or 83 g·cm² or less. For high MOT embodiment,the golf ball preferably has an MOT of 86 g·cm² or greater, or 87 g·cm²or greater. MOT is measured on a model MOI-005-104 Moment of InertiaInstrument manufactured by Inertia Dynamics of Collinsville, Conn. Theinstrument is connected to a PC for communication via a COMM port and isdriven by MOT Instrument Software version #1.2.

Thermoplastic layers herein may be treated in such a manner as to createa positive or negative hardness gradient. In golf ball layers of thepresent invention wherein a thermosetting rubber is used,gradient-producing processes and/or gradient-producing rubberformulation may be employed. Gradient-producing processes andformulations are disclosed more fully, for example, in U.S. patentapplication Ser. Nos. 12/048,665, filed on Mar. 14, 2008; 11/829,461,filed on Jul. 27, 2007; 11/772,903, filed Jul. 3, 2007; 11/832,163,filed Aug. 1, 2007; 11/832,197, filed on Aug. 1, 2007; the entiredisclosure of each of these references is hereby incorporated herein byreference.

In addition to the materials disclosed above, any of the core or coverlayers may comprise one or more of the following materials:thermoplastic elastomer, thermoset elastomer, synthetic rubber,thermoplastic vulcanizate, copolymeric ionomer, terpolymeric ionomer,polycarbonate, polyolefin, polyamide, copolymeric polyamide, polyesters,polyester-amides, polyether-amides, polyvinyl alcohols,acrylonitrile-butadiene-styrene copolymers, polyarylate, polyacrylate,polyphenylene ether, impact-modified polyphenylene ether, high impactpolystyrene, diallyl phthalate polymer, metallocene-catalyzed polymers,styrene-acrylonitrile (SAN), olefin-modified SAN,acrylonitrile-styrene-acrylonitrile, styrene-maleic anhydride (S/MA)polymer, styrenic copolymer, functionalized styrenic copolymer,functionalized styrenic terpolymer, styrenic terpolymer, cellulosepolymer, liquid crystal polymer (LCP), ethylene-propylene-diene rubber(EPDM), ethylene-vinyl acetate copolymer (EVA), ethylene propylenerubber (EPR), ethylene vinyl acetate, polyurea, and polysiloxane.Suitable polyamides for use as an additional material in compositionsdisclosed herein also include resins obtained by: (1) polycondensationof (a) a dicarboxylic acid, such as oxalic acid, adipic acid, sebacicacid, terephthalic acid, isophthalic acid or 1,4-cyclohexanedicarboxylicacid, with (b) a diamine, such as ethylenediamine,tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, ordecamethylenediamine, 1,4-cyclohexyldiamine or m-xylylenediamine; (2) aring-opening polymerization of cyclic lactam, such as ε-caprolactam orω-laurolactam; (3) polycondensation of an aminocarboxylic acid, such as6-aminocaproic acid, 9-aminononanoic acid, 11-aminoundecanoic acid or12-aminododecanoic acid; or (4) copolymerization of a cyclic lactam witha dicarboxylic acid and a diamine. Specific examples of suitablepolyamides include Nylon 6, Nylon 66, Nylon 610, Nylon 11, Nylon 12,copolymerized Nylon, Nylon MXD6, and Nylon 46.

In embodiments of the present invention wherein at least one layer isformed from a rubber composition, suitable rubber compositions includenatural and synthetic rubbers, including, but not limited to,polybutadiene, polyisoprene, ethylene propylene rubber (“EPR”), ethylenepropylene diene rubber (“EPDM”), styrenic block copolymer rubbers (suchas SI, SIS, SB, SBS, SIBS, and the like, where “S” is styrene, “I” isisobutylene, and “B” is butadiene), butyl rubber, halobutyl rubber,copolymers of isobutylene and para-alkylstyrene, halogenated copolymersof isobutylene and para-alkylstyrene, copolymers of butadiene withacrylonitrile, polychloroprene, alkyl acrylate rubber, chlorinatedisoprene rubber, acrylonitrile chlorinated isoprene rubber, andcombinations of two or more thereof. Diene rubbers are preferred,particularly polybutadienes and mixtures of polybutadiene with otherelastomers, and especially 1,4-polybutadiene having a cis-structure ofat least 40%. In a particularly preferred embodiment, the rubbercomposition is a reaction product of a diene rubber, a crosslinkingagent, a filler, a co-crosslinking agent or free radical initiator, andoptionally a cis-to-trans catalyst. The rubber is preferably selectedfrom polybutadiene and styrene-butadiene. The crosslinking agenttypically includes a metal salt, such as a zinc-, aluminum-, sodium-,lithium-, nickel-, calcium-, or magnesium salt, of an unsaturated fattyacid or monocarboxylic acid, such as (meth) acrylic acid. Preferredcrosslinking agents include zinc acrylate, zinc diacrylate (ZDA), zincmethacrylate, and zinc dimethacrylate (ZDMA), and mixtures thereof. Thecrosslinking agent is present in an amount sufficient to crosslink aportion of the chains of the polymers in the composition. Thecrosslinking agent is generally present in the rubber composition in anamount of from 15 to 30 phr, or from 19 to 25 phr, or from 20 to 24 phr.The desired compression may be obtained by adjusting the amount ofcrosslinking, which can be achieved, for example, by altering the typeand amount of crosslinking agent. The free radical initiator can be anyknown polymerization initiator which decomposes during the cure cycle,including, but not limited to, dicumyl peroxide, 1,1-di-(t-butylperoxy)3,3,5-trimethyl cyclohexane, a-a bis-(t-butylperoxy) diisopropylbenzene,2,5-dimethyl-2,5 di-(t-butylperoxy) hexane or di-t-butyl peroxide, andmixtures thereof. The rubber composition optionally contains one or moreantioxidants. Antioxidants are compounds that can inhibit or prevent theoxidative degradation of the rubber. Suitable antioxidants include, forexample, dihydroquinoline antioxidants, amine type antioxidants, andphenolic type antioxidants. The rubber composition may also contain oneor more fillers to adjust the density and/or specific gravity of thecore or cover. Fillers are typically polymeric or mineral particles.Exemplary fillers include precipitated hydrated silica, clay, talc,asbestos, glass fibers, aramid fibers, mica, calcium metasilicate,barium sulfate, zinc sulfide, lithopone, silicates, silicon carbide,diatomaceous earth, polyvinyl chloride, carbonates (e.g., calciumcarbonate and magnesium carbonate), metals (e.g., titanium, tungsten,aluminum, bismuth, nickel, molybdenum, iron, lead, copper, boron,cobalt, beryllium, zinc, and tin), metal alloys (e.g., steel, brass,bronze, boron carbide whiskers, and tungsten carbide whiskers), metaloxides (e.g., zinc oxide, iron oxide, aluminum oxide, titanium oxide,magnesium oxide, and zirconium oxide), particulate carbonaceousmaterials (e.g., graphite, carbon black, cotton flock, natural bitumen,cellulose flock, and leather fiber), microballoons (e.g., glass andceramic), fly ash, regrind, nanofillers and combinations thereof. Therubber composition may also contain one or more additives selected fromfree radical scavengers, accelerators, scorch retarders, coloringagents, fluorescent agents, chemical blowing and foaming agents,defoaming agents, stabilizers, softening agents, impact modifiers,plasticizers, and the like. The rubber composition may also contain asoft and fast agent, such as those disclosed in U.S. patent applicationSer. No. 11/972,240, the entire disclosure of which is herebyincorporated herein by reference. Examples of commercially availablepolybutadienes suitable for use in forming golf ball core layers of thepresent invention include, but are not limited to, Buna CB23,commercially available from LANXESS Corporation; SE BR-1220,commercially available from The Dow Chemical Company; Europrene® NEOCIS®BR 40 and BR 60, commercially available from Polimeri Europa; UBEPOL-BR®rubbers, commercially available from UBE Industries, Ltd.; and BR 01commercially available from Japan Synthetic Rubber Co., Ltd. Suitabletypes and amounts of rubber, crosslinking agent, filler, co-crosslinkingagent, initiator and additives are more fully described in, for example,U.S. Patent Application Publication No. 2004/0214661, 2003/0144087, and2003/0225197, and U.S. Pat. Nos. 6,566,483, 6,695,718, and 6,939,907,the entire disclosures of which are hereby incorporated herein byreference.

In embodiments of the present invention wherein at least one layer isformed from a conventional HNP composition, suitable HNP compositionscomprise an HNP and optionally additives, fillers, and/or melt flowmodifiers. Suitable HNPs are salts of homopolymers and copolymers ofα,β-ethylenically unsaturated mono- or dicarboxylic acids, andcombinations thereof, optionally including a softening monomer. The acidpolymer is neutralized to 70% or higher, including up to 100%, with asuitable cation source. Suitable additives and fillers include, forexample, blowing and foaming agents, optical brighteners, coloringagents, fluorescent agents, whitening agents, UV absorbers, lightstabilizers, defoaming agents, processing aids, mica, talc, nanofillers,antioxidants, stabilizers, softening agents, fragrance components,plasticizers, impact modifiers, acid copolymer wax, surfactants;inorganic fillers, such as zinc oxide, titanium dioxide, tin oxide,calcium oxide, magnesium oxide, barium sulfate, zinc sulfate, calciumcarbonate, zinc carbonate, barium carbonate, mica, talc, clay, silica,lead silicate, and the like; high specific gravity metal powder fillers,such as tungsten powder, molybdenum powder, and the like; regrind, i.e.,core material that is ground and recycled; and nano-fillers. Suitablemelt flow modifiers include, for example, fatty acids and salts thereof,polyamides, polyesters, polyacrylates, polyurethanes, polyethers,polyureas, polyhydric alcohols, and combinations thereof. Suitable HNPcompositions also include blends of HNPs with partially neutralizedionomers as disclosed, for example, in U.S. Patent ApplicationPublication No. 2006/0128904, the entire disclosure of which is herebyincorporated herein by reference, and blends of HNPs with additionalthermoplastic and thermoset materials, including, but not limited to,ionomers, acid copolymers, engineering thermoplastics, fattyacid/salt-based highly neutralized polymers, polybutadienes,polyurethanes, polyesters, thermoplastic elastomers, and otherconventional polymeric materials. Suitable HNP compositions are furtherdisclosed, for example, in U.S. Pat. Nos. 6,653,382, 6,756,436,6,777,472, 6,894,098, 6,919,393, and 6,953,820, the entire disclosuresof which are hereby incorporated herein by reference.

Other preferred materials suitable for use as an additional material ingolf ball compositions disclosed herein include Skypel polyesterelastomers, commercially available from SK Chemicals of South Korea;Septon® diblock and triblock copolymers, commercially available fromKuraray Corporation of Kurashiki, Japan; and Kraton® diblock andtriblock copolymers, commercially available from Kraton Polymers LLC ofHouston, Tex.

Ionomers are also well suited for blending with compositions disclosedherein. Suitable ionomeric polymers include α-olefin/unsaturatedcarboxylic acid copolymer- or terpolymer-type ionomeric resins.Copolymeric ionomers are obtained by neutralizing at least a portion ofthe carboxylic groups in a copolymer of an α-olefin and anα,β-unsaturated carboxylic acid having from 3 to 8 carbon atoms, with ametal ion. Terpolymeric ionomers are obtained by neutralizing at least aportion of the carboxylic groups in a terpolymer of an α-olefin, anα,β-unsaturated carboxylic acid having from 3 to 8 carbon atoms, and anα,β-unsaturated carboxylate having from 2 to 22 carbon atoms, with ametal ion. Examples of suitable α-olefins for copolymeric andterpolymeric ionomers include ethylene, propylene, 1-butene, and1-hexene. Examples of suitable unsaturated carboxylic acids forcopolymeric and terpolymeric ionomers include acrylic, methacrylic,ethacrylic, α-chloroacrylic, crotonic, maleic, fumaric, and itaconicacid. Copolymeric and terpolymeric ionomers include ionomers havingvaried acid contents and degrees of acid neutralization, neutralized bymonovalent or bivalent cations as disclosed herein. Examples ofcommercially available ionomers suitable for blending with compositionsdisclosed herein include Surlyn® ionomer resins, commercially availablefrom E. I. du Pont de Nemours and Company, and Iotek® ionomers,commercially available from ExxonMobil Chemical Company.

Silicone materials are also well suited for blending with compositionsdisclosed herein. Suitable silicone materials include monomers,oligomers, prepolymers, and polymers, with or without adding reinforcingfiller. One type of silicone material that is suitable can incorporateat least 1 alkenyl group having at least 2 carbon atoms in theirmolecules. Examples of these alkenyl groups include, but are not limitedto, vinyl, allyl, butenyl, pentenyl, hexenyl, and decenyl. The alkenylfunctionality can be located at any location of the silicone structure,including one or both terminals of the structure. The remaining (i.e.,non-alkenyl) silicon-bonded organic groups in this component areindependently selected from hydrocarbon or halogenated hydrocarbongroups that contain no aliphatic unsaturation. Non-limiting examples ofthese include: alkyl groups, such as methyl, ethyl, propyl, butyl,pentyl, and hexyl; cycloalkyl groups, such as cyclohexyl andcycloheptyl; aryl groups, such as phenyl, tolyl, and xylyl; aralkylgroups, such as benzyl and phenethyl; and halogenated alkyl groups, suchas 3,3,3-trifluoropropyl and chloromethyl. Another type of suitablesilicone material is one having hydrocarbon groups that lack aliphaticunsaturation. Specific examples include: trimethylsiloxy-endblockeddimethylsiloxane-methylhexenylsiloxane copolymers;dimethylhexenylsiloxy-endblocked dimethylsiloxane-methylhexenylsiloxanecopolymers; trimethylsiloxy-endblockeddimethylsiloxane-methylvinylsiloxane copolymers;trimethylsiloxyl-endblockedmethylphenylsiloxane-dimethylsiloxane-methylvinysiloxane copolymers;dimethylvinylsiloxy-endblocked dimethylpolysiloxanes;dimethylvinylsiloxy-endblocked dimethylsiloxane-methylvinylsiloxanecopolymers; dimethylvinylsiloxy-endblocked methylphenylpolysiloxanes;dimethylvinylsiloxy-endblockedmethylphenylsiloxane-dimethylsiloxane-methylvinylsiloxane copolymers;and the copolymers listed above wherein at least one group isdimethylhydroxysiloxy. Examples of commercially available siliconessuitable for blending with compositions disclosed herein includeSilastic® silicone rubber, commercially available from Dow CorningCorporation of Midland, Mich.; Blensil® silicone rubber, commerciallyavailable from General Electric Company of Waterford, N.Y.; andElastosil® silicones, commercially available from Wacker Chemie AG ofGermany.

Other types of copolymers can also be added to the golf ballcompositions disclosed herein. For example, suitable copolymerscomprising epoxy monomers include styrene-butadiene-styrene blockcopolymers in which the polybutadiene block contains an epoxy group, andstyrene-isoprene-styrene block copolymers in which the polyisopreneblock contains epoxy. Examples of commercially available epoxyfunctionalized copolymers include ESBS A1005, ESBS A1010, ESBS A1020,ESBS AT018, and ESBS AT019 epoxidized styrene-butadiene-stryene blockcopolymers, commercially available from Daicel Chemical Industries, Ltd.of Japan.

Ionomeric compositions used to form golf ball layers of the presentinvention can be blended with non-ionic thermoplastic resins,particularly to manipulate product properties. Examples of suitablenon-ionic thermoplastic resins include, but are not limited to,polyurethane, poly-ether-ester, poly-amide-ether, polyether-urea, Pebax®thermoplastic polyether block amides commercially available from ArkemaInc., styrene-butadiene-styrene block copolymers,styrene(ethylene-butylene)-styrene block copolymers, polyamides,polyesters, polyolefins (e.g., polyethylene, polypropylene,ethylene-propylene copolymers, ethylene-(meth)acrylate,ethylene-(meth)acrylic acid, functionalized polymers with maleicanhydride grafting, epoxidation, etc., elastomers (e.g., EPDM,metallocene-catalyzed polyethylene) and ground powders of the thermosetelastomers.

Also suitable for forming the center and outer core layers are thecompositions having high COR when formed into solid spheres disclosed inU.S. Patent Application Publication No. 2003/0130434 and U.S. Pat. No.6,653,382, the entire disclosures of which are hereby incorporatedherein by reference. Reference is also made to U.S. Patent ApplicationPublication No. 2003/0144087 for various ball constructions andmaterials that can be used in golf ball core, intermediate, and coverlayers.

Additional materials suitable for forming the core layers include thecore compositions disclosed in U.S. Pat. No. 7,300,364, the entiredisclosure of which is hereby incorporated herein by reference. Forexample, suitable center and outer core materials include HNPsneutralized with organic fatty acids and salts thereof, metal cations,or a combination of both. In addition to HNPs neutralized with organicfatty acids and salts thereof, core compositions may comprise at leastone rubber material having a resilience index of at least about 40.Preferably the resilience index is at least about 50. Polymers thatproduce resilient golf balls and, therefore, are suitable for thepresent invention, include but are not limited to CB23, CB22,commercially available from of Bayer Corp. of Orange, Tex., BR60,commercially available from Enichem of Italy, and 1207G, commerciallyavailable from Goodyear Corp. of Akron, Ohio. Additionally, theunvulcanized rubber, such as polybutadiene, in golf balls preparedaccording to the invention typically has a Mooney viscosity of betweenabout 40 and about 80, more preferably, between about 45 and about 65,and most preferably, between about 45 and about 55. Mooney viscosity istypically measured according to ASTM-D1646.

In addition to the above materials, the center can be formed from a lowdeformation material selected from metal, rigid plastics, polymersreinforced with high strength organic or inorganic fillers or fibers,and blends and composites thereof. Suitable low deformation materialsalso include those disclosed in U.S. Patent Application Publication No.2005/0250600, the entire disclosure of which is hereby incorporatedherein by reference.

EXAMPLES

It should be understood that the examples below are for illustrativepurposes only. In no manner is the present invention limited to thespecific disclosures herein.

Additional Examples of Suitable HNPs

The HNPs of Table 1 below have been found to be particularly useful asthe relatively soft HNP and/or the relatively hard HNP of the presentinvention.

TABLE 1 Flexural Hardness**, Hardness**, cation Modulus*, Shore C ShoreD Example source psi (18 day) (annealed) 1 Ca/Mg 71,600 88 57 2 Ca/Li70,300 89 58 3 Ca 70,100 92 60 4 Ca/Zn 60,400 88 58 5 Mg 38,300 84 52 6Mg 27,600 84 52 7 Mg 16,300 78 45 8 Mg 10,600 70 40 9 Mg 10,400 69 39*Flexural modulus was measured according to ASTM D790-03 Procedure B.**Hardness was measured according to ASTM D2240.

In embodiments of the present invention directed to a golf ball havingcenter formed from a relatively soft HNP composition, Examples 6-9 areparticularly suitable for use as the relatively soft HNP composition.

In embodiments of the present invention directed to a golf ball havingan outer core layer formed from a relatively soft HNP composition,Examples 5-9 are particularly suitable for use as the relatively softHNP composition.

In embodiments of the present invention directed to a golf ball having acenter formed from a relatively hard HNP composition, Examples 1-6 areparticularly suitable for use as the relatively hard HNP composition.

In embodiments of the present invention directed to a golf ball havingan outer core layer formed from a relatively hard HNP composition,Examples 1-4 are particularly suitable for use as the relatively hardHNP composition.

Additional Examples of Suitable Ionomeric Cover Layer Compositions

Twelve ionomeric inner cover layer compositions according to the presentinvention were prepared by melt blending Surlyn® 8150 and Fusabond® 572Din a twin screw extruder, at a temperature of at least 450° F. (230°C.). The relative amounts of each component used are indicated in Table2 below.

Flex bars of each blend composition were formed and evaluated forhardness according to ASTM D2240 following 10 days of aging at 50%relative humidity and 23° C. The results are reported in Table 2 below.

TABLE 2 Fusabond ® Shore C Surlyn ® 8150, 572D, Hardness at Example wt %wt % 10 Days 1 89 11 91.2 2 84 16 89.8 3 84 16 90.4 4 84 16 89.6 5 81 1988.9 6 80 20 89.1 7 78 22 88.1 8 76 24 87.6 9 76 24 87.2 10 73 27 86.611 71 29 86.7 12 67 33 84.0

When numerical lower limits and numerical upper limits are set forthherein, it is contemplated that any combination of these values may beused.

All patents, publications, test procedures, and other references citedherein, including priority documents, are fully incorporated byreference to the extent such disclosure is not inconsistent with thisinvention and for all jurisdictions in which such incorporation ispermitted.

While the illustrative embodiments of the invention have been describedwith particularity, it will be understood that various othermodifications will be apparent to and can be readily made by those ofordinary skill in the art without departing from the spirit and scope ofthe invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the examples and descriptions setforth herein, but rather that the claims be construed as encompassingall of the features of patentable novelty which reside in the presentinvention, including all features which would be treated as equivalentsthereof by those of ordinary skill in the art to which the inventionpertains.

1. A golf ball consisting essentially of: (a) a center having a diameterof from 1.20 inches to 1.30 inches, a center hardness of 50 Shore C orgreater, and formed from a first HNP composition, the first HNPcomposition having a material hardness of 55 Shore D or less andcomprising a highly neutralized ethylene/(meth)acrylic acid/alkyl(meth)acrylate copolymer; (b) an outer core layer having a surfacehardness of 75 Shore C or greater and formed from a second HNPcomposition, the second HNP composition having a material hardness of 45Shore D or greater and comprising a highly neutralizedethylene/(meth)acrylic acid copolymer; (c) an inner cover layer; and (d)an outer cover layer; wherein the material hardness of the first HNPcomposition is less than the material hardness of the second HNPcomposition.
 2. The golf ball of claim 1, wherein the surface hardnessof the outer core layer is at least 20 Shore C units greater than thecenter hardness.
 3. The golf ball of claim 1, wherein the outer coverlayer has a material hardness less than the surface hardness of theouter core layer.
 4. The golf ball of claim 1, wherein the center has acenter hardness of from 55 Shore C to 70 Shore C.
 5. The golf ball ofclaim 1, wherein the surface hardness of the outer core layer is 85Shore C or greater, and the inner cover layer has a material hardness of90 Shore C or less.
 6. The golf ball of claim 1, wherein the surfacehardness of the outer core layer is 90 Shore C or greater, and the innercover layer has a material hardness of 90 Shore C or less.
 7. The golfball of claim 1, wherein the core has an overall dual core compressionof from 75 to
 90. 8. The golf ball of claim 1, wherein the core has anoverall dual core diameter of from 1.52 inches to 1.59 inches.
 9. A golfball consisting essentially of: (a) a center having a diameter of from0.75 inches to 1.19 inches, a center hardness of 50 Shore C or greater,and formed from a first HNP composition, the first HNP compositionhaving a material hardness of 55 Shore D or less and comprising a highlyneutralized ethylene/(meth)acrylic acid/alkyl (meth)acrylate copolymer;(b) an outer core layer having a surface hardness of 75 Shore C orgreater and formed from a second HNP composition, the second HNPcomposition having a material hardness of 45 Shore D or greater andcomprising a highly neutralized ethylene/(meth)acrylic acid copolymer;(c) an inner cover layer; and (d) an outer cover layer; wherein thematerial hardness of the first HNP composition is less than the materialhardness of the second HNP composition.
 10. The golf ball of claim 9,wherein the surface hardness of the outer core layer is at least 20Shore C units greater than the center hardness.
 11. The golf ball ofclaim 9, wherein the outer cover layer has a material hardness less thanthe surface hardness of the outer core layer.
 12. The golf ball of claim9, wherein the center has a center hardness of from 55 Shore C to 70Shore C.
 13. The golf ball of claim 9, wherein the surface hardness ofthe outer core layer is 85 Shore C or greater, and the inner cover layerhas a material hardness of 90 Shore C or less.
 14. The golf ball ofclaim 9, wherein the surface hardness of the outer core layer is 90Shore C or greater, and the inner cover layer has a material hardness of90 Shore C or less.
 15. The golf ball of claim 9, wherein the core hasan overall dual core compression of from 75 to
 90. 16. The golf ball ofclaim 9, wherein the diameter of the center is from 0.850 inches to1.150 inches.
 17. The golf ball of claim 9, wherein the diameter of thecenter is from 0.875 inches to 1.125 inches.
 18. The golf ball of claim9, wherein the core has an overall dual core diameter of from 1.52inches to 1.59 inches.